In the wafer processing schemes used in the semiconductor industry, LPCVD reactors are generally hot wall, reduced pressure reactors that consist of a quartz tube heated by a furnace, typically comprising infrared heating elements, with process gas introduced into one end and pumped out to a vacuum pump at the other end. Pressures in the reaction chamber are typically 0.25 to 2.0 Torr (30 to 250 Pa) with temperatures ranging between 300.degree. and 700.degree. C. and gas flows between 100 and 1000 std. cm.sup.3 /min. (sccm). The reactions of the gases at high temperatures and low pressures cause thin layers of materials with desirable properties to be deposited on the surfaces of silicon wafers placed within the LPCVD reactor.
Attempts have been made to run LPCVD equipment at temperatures above 700.degree. C., but prolonged runs at these high temperatures rapidly deteriorates the silicone "O" rings in the end caps that seal either end of the quartz reactor tube. The O-rings come apart by drying and cracking due to the high temperatures.
This O-ring deterioration can occur in less than a day at processing temperatures higher than 700.degree. C. causing extended down time of the LPCVD reactor tube and accompanying hold up of the wafer process flow. One approach to this problem has been to somehow cool down the end caps so that the O-rings will not become overheated. It is becoming increasingly important to run LPCVD reactors at higher temperatures due to the discoveries of new processes that run efficiently only at these higher temperatures.
One commercially available solution is an end cap that has a single pass of stainless steel tubing wrapped around the circumference or positioned in a loop on the end of the end cap. Such tubing is typically only spot welded to the end cap so that there are very few intimate contact points between the end cap and the tubing. While a heat exchange fluid, such as water, can do a very efficient job of cooling the tubing, the end cap itself is not cooled very well due to the indirect contact of the system.
The present inventors tried a number of approaches to solve the problem. A suggested improvement on the commercially available system was to add a "heat sink" compound or paste between the tubing and the end cap, such as a metal-filled epoxy. However, such a technique would have been rather messy and cumbersome to accomplish and may not actually have improved the heat transfer surface area appreciably. Another approach was to machine grooves into the outer circumference of the end cap for the tubing to lay in. However, then it was discovered that machining grooves that tubing would lay in and make intimate contact with the end cap was physically difficult. Still another idea was to wrap tubing around the end cap and slide a sleeve over the tubing to force better contact. Even this concept was physically awkward.